1. Field of the Invention
The present invention relates to a semiconductor device having a circuit including a thin film transistor (hereinafter, referred to as a TFT) and a manufacturing method thereof. For example, the invention relates to an electronic device equipped with a light emitting display device having a TFT and an organic light emitting element, as a part.
Note that in this specification, a semiconductor device means overall devices which can function by using semiconductor properties. An electro-optical device, a semiconductor circuit and an electronic device are all included in the semiconductor device.
2. Description of the Related Art
Recently, research on a light emitting device having an EL element as a self-luminous light emitting element has been activated. This light emitting device is also referred to as an organic EL display or an organic light emitting diode. The light emitting device has characteristics such as fast response speed suitable for movie display, or low voltage and low power consumption driving. Therefore, the light emitting device draws attention as a next generation display including a new-generation portable telephone or a personal digital assistance (PDA).
An EL element has a structure in which a layer containing organic compound (hereinafter, referred to as an EL layer), adopted as an emission layer, is interposed between an anode and a cathode. Electroluminescence is produced from the EL layer by applying an electric field to the anode and the cathode.
A low-molecular weight material or a high-molecular weight material can be used for the EL layer in the EL element. A vapor deposition (including a vacuum vapor deposition), a spin coating method, an ink-jet method, a dip method, an electric field polymerization method, or the like is employed as a method for forming the EL layer.
In the case of manufacturing a full-color flat panel display using emission colors of red (R), green (G), and blue (B), a space between different pixels is designed to be wide or an insulator referred to as a bank (or a barrier) is disposed between pixels since the film formation by the above-described film formation method is not so accurate.
In the patent document 1, the applicant describes a structure in which a light-extraction efficiency is improved by disposing a light shielding portion on the edge of an EL element to shield light to be emitted from a transparent electrode to the light shielding portion. Note that in the patent document 1, a light emitting device having a bottom emission structure is described. (Patent Document 1: Japanese Patent Application Laid-Open No. 2002-83689)
In the patent document 2, the applicant proposes to prevent reflected light by a wiring from reaching eyes of an observer by using a light-absorbing multilayer film as a top layer of a bank and using an organic resin as a bottom layer. Note that in the patent document 2, a light emitting device having a top emission structure is described. (Patent Document 2: Japanese Patent Application Laid-Open No. 2004-31201)
In addition, in the patent document 3, the applicant describes a structure in which a shielding film is disposed adjacent to an anode or a cathode of a light emitting element in order to prevent an EL light emitting device from having a mirror surface without using a circularly-polarizing film. Note that in the patent document 3, a light emitting device having a top emission structure and a bottom emission structure is described. (Patent Document 3: Japanese Patent Application Laid-Open No. 2002-33185)
A full-color flat panel display using emission colors of red, green, and blue is increasingly required to have higher definition, higher aperture ratio, and higher reliability. Such requirements a are a major object in miniaturizing each display pixel pitch to make a light emitting device highly precise (increasing the number of pixels) and downsized. Simultaneously, increasing the productivity and lowering the cost are required.